The principle of effective stress states that the strength and volume change behaviors of soil are governed by intergranular forces expressed in terms of a continuum quantity called effective stress. Past research on effective stress formulations has identified a tensorial quantity that characterizes the liquid phase of unsaturated granular geomaterials. This quantity was named fabric tensor of the liquid phase and was shown to be anisotropic and to have an intrinsic association with the evolution of the effective stress tensor. It was also shown that its variation is random and can be depicted with microstructural image analysis. In this study, two past micromechanical effective stress formulations are discussed in comparison with Bishop's effective stress. The extended Mohr-Coulomb and effective stress approaches are used in interpreting shear strength parameters and effective stress parameter for partially saturated granular soils. Correlations are identified for some material variables. The nonlinearity observed in the angle of friction associated with the matric suction was discussed in relation to the fabric tensor of the liquid phase.
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